Is AC3 passthru completely lossless?

[KyleMadrid]

I know this is obviously a 'video help' forum, but I though it would be okay if I asked this question here...

Anyway, I often encode 1080i videos which have AC3 as the original audio codec, and I don't like to lose any audio quality when encoding, and I've read that AC3 passthru is completely lossless and will be exactly the same as the source, but I've also read that AC3 passthru is very good, but not exactly lossless.

Can someone please tell me if it is actually completely lossless or not?

Thanks in advance

[smrpix]

By definition passthrough means just that, pass it through, don't touch it.

Don't know what software you're using, but the ones I use treat it that way.

[KyleMadrid]

By definition passthrough means just that, pass it through, don't touch it.

Don't know what software you're using, but the ones I use treat it that way.

Yeah, I understand, and up until 10 minutes ago I always thought it was lossless, but I just read an article which stated that it was very good but not quite lossless, so I just wanted to clarify.

thanks for your quick reply.

[hech54]

By definition passthrough means just that, pass it through, don't touch it.

Don't know what software you're using, but the ones I use treat it that way.

Yeah, I understand, and up until 10 minutes ago I always thought it was lossless, but I just read an article which stated that it was very good but not quite lossless, so I just wanted to clarify.

thanks for your quick reply.

Proper passthru IS LOSSLESS. AC3 itself is NOT lossless. You read the "article" incorrectly.

[Selur]

Out of curiosity: Which article?

[KyleMadrid]

Out of curiosity: Which article?

http://lifehacker.com/5559007/the-hassle+free-guide-to-ripping-your-blu+ray-collection

Scroll down to where it says "Step Three: Set Your Quality Settings and Encode" and you will see where he talks about audio encoding.

[mike20021969]

And you still haven't mentioned what software you're using.

[Selur]

From the looks of it the author probably was refering to the recompression of the audio, but I agree like it is not so clear what he is referring to.
@mike20021969: the article uses handbrake

[Island_Dweller]

It will likely be some form of either AC3 or DTS—there are a few different versions of each, but for each I recommend choosing the Passthru option for your Audio codec (AC3 Passthru or DTS Passthru). It isn't lossless, but it's pretty darn good and is by far the simpler option (lossless audio would require more software, more time, and more space, so we won't go into it in this how-to).

If that's the part you're worried about, don't be.

The passthrough process is lossless, as in, what's on the disc is copied to your finale file without alteration. But regular ac3 or DTS core found on blurays do not use lossless compression, as say flac does.